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I'll give an example, to make my question a bit more clear.

If I have e 12Mpx camera (D700, always shooting in raw format), the highest possible resolution is 4256 × 2832. Obviously, in most cases, if the image size is reduced, say twice (to 2128 x 1416), the picture would look much better (on the screen at least, 100% view).
2128 x 1416 printed using 160 DPI would give 13.3 x 8.85 inches.

Similar thing can be achieved by simly increasing the DPI twice.
So, 4256 × 2832 printed using 320 DPI would give again 13.3 x 8.85 inches.

The final sizes are the same. Here are my concerns:

  • obviously, higher DPI means more details (but ...)
  • but reducing the size of the image will "hide" some "bad" things (would look like the noise is less, the image is sharper, more contrast, etc.

So, these 2 things make me think, reducing the size and printing at lower DPI would be better or I'm wrong?

Of course, combing both things will be best (I think), but this will make the print smaller that I'd like it to be.

I know for large prints, if looked from some distance, 320 is not necessary, but I'm talking about some small prints, like ones for album (like A4 and smaller). My point is - the prints will be watched really close.


I can't easily test this and even if I could, I think this would depend on the printer. That's why I decided to ask for advice.

Please consider - the printer is professional and much higher DPI can be used.

share|improve this question
2  
Possibly answered by: Extreme Digital Upscaling –  jrista Dec 16 '13 at 13:41
1  
Also useful: Generating High Quality Ink Jet Prints –  jrista Dec 16 '13 at 13:42
    
@jrista - thanks for the link, I found that question some minutes ago and will read it a bit later. –  Kiril Kirov Dec 16 '13 at 13:43

2 Answers 2

up vote 3 down vote accepted

If the physical size of the prints isn't changing, i.e. remaining 13.3 x 8.85 inches, then I would say stick to the larger image at 320 DPI. If you print the same size image at 160 versus 320 you'll have less printed dots per inch, meaning the physical resolution of the print is smaller, and I would argue the lines and curves in the image would appear less smooth at 160, and colour tones would graduate less smoothly too.

Have you thought about what might happen if you brought the resolution of the image down even further? let's say we halved it one more time, and then again, to 532 x 354. Would you print a 13.3 x 8.85 inch photograph at 40 DPI? Taking this further, you could arguably get down to only a few dots per inch. I'm confident the photo would look a lot less like a photo and just a splotch of colour.

Reducing the pixels on screen doesn't eliminate noise or other image artefacts - it just conceals them from your eyes. To achieve this effect in print, you need to pack more dots into an inch. The higher the number of pixels you have, the easier it is to pack more dots into every inch. If you have a 4256 x 2832 pixel image, and you printed at 320 DPI, you'd have a 13.3 x 8.85 inch photograph. If you printed that same image at 600 DPI, you'd have a 7.09 x 4.72 inch photograph. The latter would be smaller, but it would achieve the same visual effect as the on-screen pixel reduction.

Cheers

share|improve this answer
    
"Would you print a 13.3 x 8.85 inch photograph at 40 DPI" - of course not, but 40 is far from acceptable, while 160 is. My question was about reasonable increasing/decreasing of the DPI/size. This doesn't sound reasonable. I know I didn't mention that, but I think it's understandable.. –  Kiril Kirov Dec 16 '13 at 13:39
1  
"Reducing the pixels on screen doesn't eliminate noise or other image artefacts" - I know. I didn't say it does. I said "hide" and even in quotes. Thanks for the answer. I've never printed anything yet, although photography is my hobby for several years. I intend to "fix this mistake" :) –  Kiril Kirov Dec 16 '13 at 13:40
    
Decreasing the DPI count hides the artifacts because you're eliminating details from your image. If what you want is a blurry non-detailed image, then why do you use such a high pixel count? –  fernando.reyes Dec 16 '13 at 17:32
    
My apologies Kiril, my answer may seem a bit rude. I was just trying to get you to think about the impact to your prints of reducing your pixel count and maintaining the same physical size print. The result is never better than the former. The basic rule is, more DPI if you have the available pixels. You are right, for some purposes 160 DPI is acceptable, but you mentioned you had a professional printer capable of many more DPI, and that your prints would be looked at closely. Based on this information, it's never wise to reduce DPI, and in my honest opinion I think 160 is low for any prints. –  Aleks Danger Dec 16 '13 at 18:48
    
You're also right in that you said to "hide." While this effect works on screen, it won't have the same impact on print where the physical size is the same. Try reducing the pixel count of an image, and then blowing it up to the same on-screen size as the original image - you'll immediately see a decrease in image quality.Same with print, it will lose quality. Your question was clearly, "So, these 2 things make me think, reducing the size and printing at lower DPI would be better or I'm wrong?" and my answer is no, less pixels and DPI for the same physical size print is not better - it's worse –  Aleks Danger Dec 16 '13 at 18:56

The less modification you make the more the final result is degraded. That is the basic.

But, some action enhance several part for your perception (like all the gadget of lightroom or any corrective application) or to conterpart limitation of process until the final print (like a poor driver for the printer or a limited printer gamma, ...).

Thus the answer will depend highly of your process chain and perception.

A camera with 12 Mp taht use poor JPEG compression (in quality, not necessary in size/ratio) will give bad image at source and reduction of dpi/size with a good soft (like photoshop) will give the impression of better image taht may give a good looking print because color correction and artifact are removed but with less detail also.

Keep big (original) of all element as long as you can in the chain of print process and don't trust your display too much (especially without decent hardaware and calibration).

share|improve this answer
    
Sorry should have mentioned - I'm talking about D700 & raw format (updated question). So, your advise is - don't reduce size, but increase DPI at the final stage - printing? –  Kiril Kirov Dec 16 '13 at 14:46
    
increase DPI (pixel quantity in fact) without special action on it that modify the content is just a source of problem. Main case to use could be that a following process inthe chain does not accept the original DPI info or miss the upscaling (poor software conversion like low budget printer [driver]) so a modification earlier, under control could be preferable. The advice is to try to stay as long as possible with original caracteristic of the picture (number of pixel and protocol of storage because size/DPI is just a indication how to handle pixel) –  NeronLeVelu Dec 17 '13 at 7:15

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